Chemical mechanical polishing (CMP) is known as a polishing method used for mirror finishing a semiconductor wafer, and planarizing the surface of an insulating film and a conductive membrane of a semiconductor device. CMP is a method in which the surface of a material to be polished such as a wafer is polished with a polishing pad by using a polishing slurry (hereinafter also simply referred to as “slurry”) containing abrasive grains and a reaction liquid.
Conventionally, a non-woven fabric-type polishing pad has been widely used as the polishing pad for CMP. The non-woven fabric-type polishing pad is a flexible polishing pad including a non-woven fabric impregnated with polyurethane. Due to its flexibility, the non-woven fabric-type polishing pad has an advantage of having good contact with a material to be polished. It also has an advantage of having good slurry retention because the non-woven fabric has voids. On the other hand, the non-woven fabric-type polishing pad has a disadvantage of exhibiting a low performance in planarizing the surface to be polished (hereinafter referred to as “planarization performance”) due to its flexibility. The non-woven fabric-type polishing pad also has a disadvantage that scratching is likely to occur on the surface to be polished when the voids of the non-woven fabric are clogged by abrasive grains and polishing debris. Another disadvantage is that abrasive grains and polishing debris cannot be sufficiently removed by washing when they have entered deeply into the voids of the non-woven fabric, resulting in a short life.
A polishing pad composed mainly of a polymer foam having a closed-cell structure is also known as a polishing pad of a type different from the non-woven fabric-type polishing pad. The polishing pad composed mainly of a polymer foam has a higher hardness than the non-woven fabric-type polishing pad, and thus exhibits an excellent planarization performance. Since the polishing pad composed mainly of a polymer foam has a closed-cell structure, abrasive grains and polishing debris cannot easily enter deeply into the voids unlike the case of the non-woven fabric-type polishing pad. Therefore, abrasive grains and polishing debris can be relatively easily removed by washing, resulting in a relatively long life. As the polishing pad composed mainly of a polymer foam, for example, polishing pads as disclosed in PTLs 1 to 6 below are known that include, as a polishing layer, a foamed polyurethane molded article obtained by foaming and molding a two-liquid curable polyurethane by casting. The foamed polyurethane molded article is preferably used as a polishing layer due to its excellent abrasion resistance.
Semiconductor devices include integrated circuits with a high level of integration and multilayered interconnections. Polishing pads used for a planarization process for semiconductor devices are required to exhibit a higher planarization performance. A polishing pad that exhibits a high planarization performance is a polishing pad that offers a high polishing rate for a portion to be polished and a low polishing rate for a portion that is not to be polished. The polishing pad that exhibits a high planarization performance is required to have a high hardness. A polishing pad including a foamed polyurethane molded article as a polishing layer exhibits a high planarization performance because the polishing layer has a relatively high hardness.
With a further increase in the level of integration and the number of multilayered interconnections in semiconductor devices in recent years, there is a need for a polishing pad that exhibits an even higher planarization performance. In the case of using a polishing pad including a foamed polyurethane molded article as a polishing layer, it has been difficult to achieve a high planarization performance by further increasing the hardness of the polishing layer. In order to provide a polishing pad that offers an even higher planarization performance, for example, PTLs 7 and 8 below disclose high-hardness polishing pads composed mainly of an unfoamed resin.